Antiques traders fear the death of Portobello Market "within five years" after the opening of the street's biggest chain store.

The two-storey branch of fashion retailer AllSaints launched last month in a former arcade where more than 150 traders, including a 94-year-old woman, made a living until last summer.

Local campaigners say Kensington & Chelsea council's failure to save the former Lipka's Antiques Arcade made a mockery of its pledge to ensure the market is "not overrun by identikit multiples".

The AllSaints store, which is decorated with antique Singer sewing machines and has a warehouse feel with wooden floors and dim lighting, covers the basement and ground floor of its 15,000 sq ft site — the length of six shop-fronts along Westbourne Grove and four down Portobello Road.

Antiques traders warn it is only a matter of time before other stalls are driven out. They accuse the area's dominant landlord, Warren Todd —whose firm Westbourne Arcades owns the AllSaints site — of jeopardising the market in his pursuit of high rents.

Geoff Knowles, treasurer of the Portobello Antiques Dealers Association, said: "The traders respect the right of the owner to earn a living. The thing that stinks is that the market which used to be there is how he made his money in the first place."

Robina Rose, a founder of campaigners Friends of Portobello, said: "To sell Portobello down the river means it will be gone in less than five years."

The arrival of AllSaints comes less than three years after a key report from a retail commission set up by Kensington & Chelsea council to find ways of protecting small shops.

One member, former Kensington & Chelsea mayor Tim Ahern, said the council had no legal right to intervene because there had not been a change of use at the site. He said one possible measure was for the council to buy up antique arcades to keep them open.

An AllSaints spokesman said: "We've had nothing but good reviews for this store. It's bringing trade to the area. We put antique sewing machines in the windows to stay in keeping with the local aesthetic."